What number makes this equation true?
Explanation: ${?}-{435}= 210}$ ${210}$ ${?}$ $-435$ What number can we subtract ${435}$ from and be left with $210}?$ We can add ${435}$ to $210}$ to find the missing number. $\begin{aligned}{{435}}&\\ \underline{+210}} &\\ {645}&\end{aligned}$ ${210}$ ${645}$ $-435$ $+435$ ${645}-435=210$